The actress revealed the news while speaking to The Sunday Times, when she said: “I was thrilled when the Downton offer came.”

Actress Simone Lahbib, of Bad Girls fame, has also joined the cast as another servant.

The third series of the popular drama will begin in September on ITV.

Commenting on what to expect from the third series, creator Julian Fellowes has also said that it will focus largely on the family’s financial woes and the troubles in Ireland.

Speaking at the PBS Television Critics’ press tour in America, Fellowes said: “The ’20s are a more nebulous time. In the third series you see the impact on this family of the Irish Troubles.

“That really started up after the end of the First World War, and actually, at the time, was much more the headline than the suffragettes or the other things.

“The Irish problem seemed to be a kind of yawning difficulty for the British empire and everything. But, you know, again I don’t think a lot of people know about that. It’s rather nice to go into that.”